This invention relates to a member that can be used as a fusing roller for hot pressure fixing of toner particles or as an intermediate member in transfuse systems. It relates in particular to such a roller with specified elastomeric layers, in particular silicone rubbers.
In electro(photo)graphic copiers or printers, the toner image formed on the photoconductor can be transferred directly to the final image receiver, e.g. plain paper whereon it is fixed by fusing the toner particles by heat and pressure using fixing rollers. The toner image formed on the photoconductor or brought on a means for collecting the colour separations when performing colour printing, can be transferred not directly to the final image receiving member but in a first transfer zone to an intermediate member that can be heated and from that intermediate member to the final image receiving member whereon it is fixed by the heating of the intermediate member that is pressed against the final image receiving member by a pressure means. This latter process is further on termed as a xe2x80x9ctransfusexe2x80x9d and the intermediate member is designated by xe2x80x9ctransfusing memberxe2x80x9d.
Fusing and fixing of toner particles to a substrate by simultaneous application of heat and pressure are well known in the art and also fusing rollers for use in hot pressure fixing of toner particles are well known.
In, e.g., U.S. Pat. No. 4,078,286 a fusing roller is disclosed with a base member and thereon a first layer of an heat resistant resin and on top of the first layer a layer of silicone rubber.
In U.S. Pat. No. 4,257,699 and its equivalent EP-Axe2x80x94018 140 a fuser member with a base material and two elastomer layers thereon, the outer elastomer layer containing a metal filler is disclosed. In U.S. Pat. No. 5,049,444 a multi-layered fusing member is disclosed. This member has in sequential order a base support member, an adhesive layer, a tie coat layer and an outer elastomeric fusing layer with therein a copolymer with vinylidene fluoride and a metal oxide.
Also transfusing members are well known in the art. When transfusing members are in contact with the photoconductor it is important that the photoconductor is not soiled by impurities present in the final imaging member. Therefore transfusing members comprising two layers, a top layer permeable for the impurities and a layer under the top layer absorbing the impurities have been disclosed. In, e.g., EP-A-146 980 a transfusing member is described consisting of a metal roller provided with a first covering of pigmented RTV silicone rubber (RTV201/200, wherein silica particles are present) and a second covering of non-pigmented silicone rubber obtained by cross-linking an xcex1,xcfx89-hydroxy-polymethylsiloxane with a tetra-ethyl silicate under influence of di-butyl tin dilaurate.
In EP-A-581 365 a transfusing member is disclosed consisting of a support with a pigmented rubber layer, wherein the pigment is preferably carbon black, and a top layer of silicone rubber.
In most of the applications of both a fusing roller and a transfusing member, a release agent, most frequently a silicone oil, is applied to the fusing or transfusing members to prevent hot-offset (i.e. toner particles adhering to the surface of the fusing or transfusing members instead of to the substrate) and to enhance the lifetime of the surface of the fusing and transfusing members.
The use of a release agent can however create problems in the finished image, basically because it gives kind of gloss to the image and that, when the release agent is not evenly spread over the image differences in gloss appear. Thus the use of release agents frequently entails problems of streaks, oily look, patchiness, etc. in the finished image. When silicone oil is applied to a transfusing member that comes in direct contact with the photoconductor, the photoconductor can be soiled by the silicone oil and therefore it is important that the use external release agent can be minimised or preferably avoided.
It has been proposed, for avoiding hot-offset when using a low amount of release agent, to change the properties of the toner particles, especially the type of toner resin that is used. Such toner particles have been disclosed in, e.g., EP-A-712 881 and EP-A-740 217. These measures do indeed offer the possibility of hot-pressure fixing even when using very low amounts of release agent, but because of the need to use special toner resins, the degrees of freedom in toner design, e.g., with respect to mechanical strength, chargeability, etc., are diminished.
Therefore the need for fusing and/or transfusing members that can be used, when only small amounts of release agent is used, is still there.
It is an object of this invention to provide a fusing member that can be used in hot-pressure fixing of toner particles to a substrate while avoiding the use of substantial amounts of release agents on the surface of the fusing member.
It is a further object of the invention to provide a fusing member that can be used in hot-pressure fixing of toner particles to a substrate while avoiding the use of substantial amounts of release agents on the surface of the fusing member that can be for a very long time preparing a large amount of prints before hot-offset appears.
It is an other object of the invention to provide a method for hot-pressure fixing of toner particles wherein only small amounts of release agent are applied to the fusing roller.
Further objects and advantages of the invention will become clear from the detailed description hereinafter.
The objects of the invention are realised by providing a fusing member comprising a support, and on said support,
an outermost layer containing a silicone elastomer, with at most 5% by weight of filler particles, said elastomer layer having a swelling factor, SF, equal to or higher than 3 and a thickness between 5 and 500 xcexcm, both limits included and
a second layer with an impurity absorbing material, closer to said support and immediately in contact with said outermost layer, said second layer being at least 40 xcexcm thick. Preferably said second layer has silicone containing elastomer and contains at least 5% by weight of metal oxide particles having a specific surface of xe2x89xa730 m2.
The objects of the invention are further realised by providing an imaging method comprising the steps of:
image-wise applying toner particles to a substrate and
fixing said toner particles to said substrate by simultaneous application of heat and pressure, characterised in that:
said fixing proceeds in a fusing system wherein a fusing member is present comprising
a support, and on said support,
an outermost layer containing a silicone elastomer, with at most 5% by weight of filler particles, said elastomer layer having a swelling factor, SF, equal to or higher than 3 and a thickness between 5 and 500 xcexcm, both limits included and
a second layer with an impurity absorbing material, closer to said support and immediately in contact with said outermost layer, said second layer being at least 40 xcexcm thick and
that at most 320 mg/m2 of a release agent is applied to the surface of said fusing roller.
As described above, during fusing and transfusing a release agent, most frequently a silicone oil, is applied to the fusing or transfusing members to prevent hot-offset (i.e. toner particles adhering to the surface of the members instead of to the substrate) and to enhance the lifetime of the surface of the fusing and transfusing members. In this document the wording xe2x80x9cfusing memberxe2x80x9d will be used to indicate both a fusing member and a transfusing member. It was now found, after experimentation, that it was possible to design a member that could be used as fusing member with a very low amount of external release agent, e.g. silicone oil, or even without any external release agent and still had a long lifetime and did not show hot-offset. Therefore the fusing member, as in the prior art, comprised two layers on a support wherein an outermost layer containing at most 5% by weight of an inorganic filler is in direct contact with a second impurity absorbing layer wherein preferably at least 5% by weight of metal oxide particles are present.
The Outermost Layer
Contrary to the prior art fusing members, however, it was found that the outermost layer of the fusing member according to this invention, had to be quite soft. Whereas in the prior art fusing members, the outermost layer is chosen to be quite hard (e.g. a hardness equal to or larger than 40 Shore A), it was now found that fusing members having an outermost layer, being between 5 and 500 xcexcm thick, with a degree of swelling factor equal to or higher than 3% gave better results in terms of avoiding hot-offset than the harder prior art outermost layers. The swelling factor is in the case of an outermost layer according to this invention an indication of the softness, a layer with a high swelling factor is quite soft. It is preferred that an outermost layer in a fusing member according to this invention has a swelling factor, SF, equal to or larger than 3, more preferably SFxe2x89xa75.
The swelling factor is measured as follows: The thickness of a self-supporting sample of the outermost layer measuring about 20 mmxc3x973 mm is measured to an accuracy of 0.1 xcexcm. This is the value Thd, standing for dry thickness. Afterwards the self-supporting sample is wetted with toluene and the sample is allowed to swell for 3 minutes, then the excess toluene is wiped and the thickness of the swollen sample is again measured to an accuracy of 0.1 xcexcm. This is the value Thw. The swelling factor, SF, is Thw/Thd.
Preferably at most 5% by weight of an inorganic filler is added to the outermost layer, more preferably at most 2% by weight of an inorganic filler is added and in an even more preferred embodiment, it no inorganic filler at all is deliberately added to the outermost layer, so that it contain no inorganic filler, except for possible impurities that can be present in the other ingredients of the layer.
Moreover it showed very beneficial to have an outermost layer having a peeling force lower than 5 N/m measured according to the Finat No 3 norm, with Tape TESA 4163 at a peeling speed of 30 cm/min. Thus peeling force is the force necessary to peel a TESA 4163 tape away from the outermost layer at a speed of 30 cm/min.
The outermost layer, which is preferably the outermost layer of the fusing member that comes in direct contact with the toner particles, contains preferably at least 80% by weight of a silicone elastomer (silicone rubber) being loosely cross-linked and forming a kind of network having a low amount of cross-links. The outermost layer may further contain, imbedded in said network a silicone oil with a molecular weight equal to or larger than 50,000. A well suited silicone oil is, e.g., the silicone oil sold by ABCR GmbH, Karlsruhe, Germany under trade name DGM-000. Very well suited elastomers, for forming the outermost layer in a fusing member of this invention, are RTV or loosely cross-linked silicone elastomers formed by poly-addition of a organopolysiloxane with average molecular weight less than 300,000 and/or an organopolysiloxane gum with average molecular weight greater than 300,000 having an alkenyl group, preferably at least two alkenyl groups, which are preferably vinyl groups. The latter silicone rubbers are preferred. Very preferred silicone rubbers for use in the outermost layer of a fusing member of this invention are silicone rubbers produced by cross-linking of organopolysiloxanes containing more than 0.005 milli-equivalent of vinyl groups per g and less than 0.1 milli-equivalent of vinyl groups per g. More preferably the content of vinyl groups in organopolysiloxanes, useful for forming the outermost layer of a fusing member of this invention, is between 0.005 and 0.05 milli-equivalent of vinyl groups per g. The equivalent value of vinyl groups is calculated by dividing the number of vinyl groups in the organopolysiloxane by the molecular weight of the organopolysiloxane.
The outermost layer can comprise a mixture of organopolysiloxanes with free alkenyl groups. In this case the average alkenyl content of the mixture is preferably between 0.005 milli-equivalent and 0.1 milli-equivalent of vinyl groups per g. More preferably the average content of vinyl groups in such a mixture of organopolysiloxanes, is between 0.005 and 0.05 milli-equivalent of vinyl groups per g. The vinyl groups on the organopolysiloxane can be terminal groups or the vinyl groups can be side groups in the organopolysiloxane. Typical examples of useful organopolysiloxanes are represented by the formulas: 
In these formulas R=alkyl or aryl group, preferably methyl, ethyl, 3,3,3-trifluorpropyl and phenyl.
Organopolysiloxanes with an alkenyl group and with average molecular weight less than 300,000 are commercially available, e.g., from Rhone-Poulenc under trade name SILCOLEASE 7420, SILCOLEASE 7440, from ABCR, Karlsruhe, Germany under trade name VGM-021. Organopolysiloxane gums with an alkenyl group and with average molecular weight greater than 300,000 commercially available, e.g., from ABCR, Karlsruhe, Germany under trade name DMS-V41, DMS-V46 and VDT-153.
The outermost layers in a fusing member according to this invention are frequently applied from a coating solution by dip-coating or by ring-coating. When doing so it is beneficial to use a mixture of a organopolysiloxane with an alkenyl group and with average molecular weight  less than 300,000 and/or an organopolysiloxane gum with an alkenyl group and with average molecular weight  greater than 300,000, since by doing so the viscosity of the coating solution can easily be adjusted for optimum coating quality without using a separate viscosity regulating compound.
The organopolysiloxane with an alkenyl group and with average molecular weight less than 300,000 and an organopolysiloxane gum with an alkenyl group and with average molecular weight greater than 300,000, forming the outermost layer of a fusing member according to this invention, can be hardened by reaction with an organopolysiloxane containing at least two hydrogen atoms direct bound to a Si-atom per-molecule. When an hardener of this type is used it is added to the coating solution so that between 0.5 to 20 moles of hydrogen atoms direct bound to a Si-atom are present per mole of the alkenyl groups.
Typical examples are: 
When preparing the outermost layer for a fusing member according to this invention, the cross-linking reaction can be speeded up by addition of a Pt-catalyser in a concentration between 0.1 to 500 ppm with respect to the total amount of organopolysiloxanes.
The outermost layer can comprise further additives, if so desired, e.g. cure retardants, heat stabilisers, flame retardants, plasticisers, anti-static agents, electric conductive compounds, etc.
The Second Layer Immediately in Contact with the Outermost Layer
The second layer comprises preferably at least 80% by weight of a silicone rubber and preferably at least 5% by weight of inorganic filler particles with specific surface of at least 30 m2/g, more preferably said particles have a specific surface of at least 50 m2/g and even more preferably said particles have a specific surface of at least 100 m2/g. This filler can be SiO2, TiO2, Al2O3, a pigment as, e.g. Cu-phthalocyanine. In a second layer of the present invention it is preferred that the inorganic filler with specific surface of at least 30 m2/g is a member selected from the group consisting of SiO2, TiO2, and Al2O3. Surprisingly, it showed that second layer carbon black as filler, did not work very well when the second layer is combined with a soft outermost layer as is the case in a fusing member of this invention. This is contrary to the disclosure of EP-A-581 365 where a second layer comprising carbon black as filler was most beneficial, when it is combined with a hard outermost layer.
The presence of the filler aids the fusing member to absorb compounds coming from the heated toner particles and/or the heated image receiving member that soil the surface of the fusing member and that penetrate the outermost layer. Thus the surface of the fusing member stays clean for a longer time of use.
The second layer is in a fusing member of this invention mostly used as the layer for transporting the thermal energy needed to fuse the toner particles from a source of heat towards the outermost layer. Therefore the thermal conductivity of the second layer is at least 0.4 W/m.K (measured according to DIN 52612 in Watt per meter times degree Kelvin), preferably the thermal conductivity of the second layer is at least 0.7 W/m.K. The high thermal conductivity is beneficial for cold offset, which means that when the fusing member has a second layer with high thermal conductivity the fusing process of the toner particles starts a lower temperatures. In order to control the thermal conductivity of the second layer in a fusing member according to this invention, this second layer further comprises preferably inorganic filler particles having an average volume diameter of at least 1 xcexcm, this larger filler particles can be silica, CuO, Fe2O3, Al2O3 etc.
The Support
The support in a fusing member of the present invention can be any support known in the art. A metal support, e.g. aluminium, stainless steel, etc., are preferred supports.
The support can be in the form of a roller, which can be a hollow metal (e.g. Al, Stainless steel, etc.) cylinder incorporating an heating source or in the form of an endless belt.
If so desired it is possible to include, in a fusing member of this invention, an adhesive layer between the support and the second layer.
The fusing member of this invention can be used in a fusing device as a heated fixing roller coupled to a pressure roller for hot pressure fixing of the toner particles. In this case, the amount of filler that can incorporated in the second layer depends whether the fusing member is used as nip-forming roller or not. When, in such a fixing device, the fusing member of this invention is used as nip-forming roller, then the amount of filler is restricted by the need for having a good elasticity of the nip-forming roller. When in such a fixing device, the pressure roller is used as nip forming roller, more filler can be added to the second layer which makes it possible to have a second layer with high thermal conductivity. It is thus preferred, in a fixing device wherein a fusing member of this invention is coupled, as fixing roller, to a pressure roller for hot pressure fixing of the toner particles that the pressure roller is the nip-forming roller, so that a second layer with high thermal conductivity can be used in the fusing member. Since the fixing roller is the heated roller in the couple fixing roller/pressure roller and it is usually heated from inside the support (which is most frequently an hollow cylinder) a second layer with high thermal conductivity is beneficial for bringing the heat rapidly to the surface of the fixing roller which in turn allows for higher fixing speed.
A fusing member of this invention can also be used as a transfusing member, in this case the toner image present on a photoconductor or on an intermediate member is not directly transferred to a final image receiving substrate and fixed there, but is first transferred to a transfusing member, from where it is further, in one step transferred and fixed to the final image receiving member. An printer using toner particles in a transfuse system is more complicated than a printer wherein direct transfer proceeds, but a transfuse system has the advantage that lower fixing temperature can be used.
In printers with transfusing systems it is often customary to avoid direct contact between the photoconductor and the transfusing member to avoid soiling of the photoconductor, therefore a toner image, developed on the photoconductor is often first transferred to an intermediate member, e.g. a belt or roller made from non-soiling material, as metal or a polymer, and from said intermediate member to the transfuse member. A fusing member of this invention can be used as transfusing member in printers with direct contact between the photoconductor as well as in printers wherein the image is transferred from the photoconductor to the transfusing member over an intermediate non-soiling member.
A fusing member according to this invention can be used in any imaging method using toner particles, e.g., electrophotography, direct electrostatic printing, ionography, magnetography, etc. A fusing member of this invention is particularly well suited in imaging method using dry toner particles with an average volume diameter between 2 and 20 xcexcm.
A fusing member of the present invention can be used with printers wherein the final image receiving substrate is in sheet form as well as in printers wherein the final image receiving substrate is in web form. A fusing member of this invention can most beneficially be used in the latter printers.
Since a fusing member of this invention can be used both a fusing roller as well as transfusing member with very low amounts of external release agent, the invention also encompasses an imaging method comprising the steps of:
image-wise applying toner particles to a substrate and
fixing said toner particles to said substrate, by simultaneous application of heat and pressure, in a fixing device with a fusing roller coupled to a pressure roller characterised in that:
said fusing roller comprises a support, and on said support,
an outermost layer containing a silicone elastomer, with at most 5% by weight of filler particles, said elastomer layer having a swelling factor, SF, equal to or higher than 3 and a thickness between 5 and 500 xcexcm, both limits included and
a second layer with an impurity absorbing material, closer to said support and immediately in contact with said outermost layer, said second layer being at least 40 xcexcm thick and
that at most 320 mg/m2 of a release agent is applied to the surface of said fusing roller.
It also encompasses an imaging method comprising the steps of xe2x80x94bringing a toner image on a transfuse member,
transferring said toner image from said member to a final image receiving substrate, and fixing said image, characterised in that
said transfusing member comprises a support, and on said support,
an outermost layer containing a silicone elastomer, with at most 5% by weight of filler particles, said elastomer layer having a swelling factor, SF, equal to or higher than 3 and a thickness between 5 and 500 xcexcm, both limits included and
a second layer with an impurity absorbing material, closer to said support and immediately in contact with said outermost layer, said second layer being at least 40 xcexcm thick and
that at most 320 mg/m2 of a release agent is applied to the surface of said transfusing member.